1. Field of the Invention
The present invention relates generally to a pneumatic starter device for controlling the initial pressurization of a pneumatic system.
II. Description of the Prior Art
Pneumatic systems of the type used in shops and manufacturing facilities typically comprise a plurality of pneumatically operated devices each having an inlet port and an exhaust port. A source of pneumatic pressure is fluidly connected to the pneumatic devices, typically through a common supply line. This supply line has an inlet end adapted for connection to the air pressure source, and a tail end.
One problem with the previously known pneumatic system occurs when the system is initially charged with pneumatic pressure as would occur, for example, at the beginning of the manufacturing day. Oftentimes, one or more pneumatic actuators have either drifted out of position or were intentially moved because of required maintenance or set up procedure. Consequently, upon the application of the pneumatic pressure to the system, these pneumatic actuators move back to their at rest position at uncontrolled speeds whenever the air pressure is reapplied. This can result in destructive forces and velocities and can cause, for example, tools left on fixtures to become flying projectiles. Similarly, fixtures that are not bolted down can be knocked off the machine while bolts can be sheared off and expensive tooling can be otherwise damaged.
In order to minimize the destructive forces and velocities which can occur when the pneumatic pressure is reapplied to the system following a system shut down, a previously known pneumatic starter device is disclosed in U.S. Pat. No. 4,402,254 to Petrimaux et al. The Petrimaux et al. patent discloses a pneumatic starter device which is connected in series between the source of pneumatic pressure and the inlet to the supply line for the pneumatic system. The tail end of tho air pressure supply line is connected as a pilot pressure to the starter device.
In operation, the Petrimaux et al. pneumatic starter device provides a restricted orifice during the initial pressurization of the pneumatic system. Whenever the pressure at the pilot port to the starter device exceeds a preset amount, the Petrimaux device valve switches to a second position in which an unrestricted port is fluidly connected in series between the pneumatic source and the fluid system.
The previously known Petrimaux device, however, is disadvantageous in two different respects. First, the Petrimaux device provides an orifice having a fixed restriction during the initial system repressurization. Since the orifice is fixed in size, the initial system pressurization can take a very long time until system pressurization is achieved. Conversely, in a less complex pneumatic device, the pressurization from the restricted port may occur too rapidly.
A second disadvantage of the previously known Petrimaux device is that the fluid pressure at the pilot port in which the Petrimaux pneumatic valve switches from its restricted to its unrestricted fluid passageway is fixed and, therefore, not user adjustable. Again, since the switching pressure is not adjustable, the fixed switching pressure of this previously known device can result in an unnecessarily long period of time for recharging the pneumatic system while, in other cases, the valve means is switched too rapidly.